Transflective liquid crystal display panels that have schemes of wide viewing angle as well as IPS (In Plane Switching) and VA (Vertical Alignment) are now-a-day popularly used and being used for liquid crystal display TVs with additional improvement of moving picture characteristics. On the other hand, the liquid crystal display (called “LCD” hereinafter) has been widely used for portable information devices such as portable phones and digital cameras. The display panels for these portable information devices are simultaneously used by one person or a few persons and therefore wide viewing angle seems not to be necessary. However considering to the application of the digital cameras, wide viewing angle is still required since the monitoring is done from the view of slant back direction. For keeping privacy of the data monitoring, some people think wide viewing angle is not necessary for the portable device applications but their ideas imply the necessity to equip a certain baffle against a look of other persons but narrow viewing angle performanceis not required.
Since the displays used for the portable information devices are used in the sunny outdoors to in dark rooms, the display panels are desired to be transflective. The transflective liquid crystal display panels have a reflective display portion and a transmissive display portion in a pixel.
The reflective display portion reflects the incident lights from the circumferences by a reflection plate. Since the contrast ratio is constant regardless the ambient brightness, good display characteristics are obtained under rather bright conditions such as those from sunny outdoors to indoors.
Since back light unit is used for the transmissive display, high contrast ratio is obtained under rather dark conditions such as those from indoors to in-darkroom.
The transflective liquid crystal displays that have both reflective display panel portion and transmissive display panel portion serve for high contrast ratio under wide ambient conditions from sunny outdoors to in-darkrooms.
The conventional transflective liquid crystal has homogeneous alignment or twisted alignment of nematic phase in the liquid crystal layer to which a voltage is applied and an electric field in a direction normal to the substrate is generated. This principal drive operation is same as that of TN (Twisted Nematic) display panel. In order to improve the contrast ratio of the liquid crystal cell which has reflective layer therein, plural phase shift plates are used. Therefore, no sufficient viewing angle characteristics have been obtained.
A transflective display panel with wide viewing angle made by an improved technology such that the transflective configuration is applied to the IPS LCD which is known as wide viewing angle transmissive display panel, is described in the reference 1.
The pixel electrodes 21 are formed in stripes in the view from the normal direction against the substrate and each part of the electrode is linked within each pixel since IPS configuration uses the electric field which is directed in parallel to the substrate. The common electrode 22 is formed in the same configuration. These topological forms as alignment of the electrodes 21 and the common electrode 22 are called comb-like electrodes.
For example, the comb-like electrodes 21 and 22 function as reflective display panel portion by exploiting them as reflective electrodes and the gap 20 functions as reflective display panel portion. The traveling light passes the liquid crystal layer twice in the reflective display panel portion but once in the transmissive display panel portion. In order to remove the difference of light path lengths for both display panel schemes, the step differences are formed between the comb-like electrodes 21 and 22 and the transmissive display panel portion has twice thickness of the liquid crystal layer against the reflective display panel portion.
In this configuration, the comb-like electrodes 21 and 22 are projected from the substrate boundary surface. The cross sectional surface of the comb-like electrodes 21 and 22 have substantially square shapes in the cross sectional plane normal to the comb-like direction. Moreover, the retardation of the liquid crystal layer is adjusted to have quarter wave length at the reflective display panel portion by adding plural phase shift plates for the purpose of improving the contrast ratio at the reflective display panel portion.
In the inventions shown in the references 2 to 4, diffusive reflection electrodes which have micro corrugation surfaces on the comb-like electrodes are used.
Reference 1;                Published Japanese Patent Application, JP, H11-242226, A (1999)        
Reference 2;                Published Japanese Patent Application, JP, 2002-139737, A (2002)        
Reference 3;                Published Japanese Patent Application, JP, 2003-21824, A (2003)        
Reference 4;                Published Japanese Patent Application, JP, 2003-21825, A (2003)        